During many medical procedures, various fluids are injected into patients for purposes of diagnosis or treatment. An example of one such fluid is contrast media used to enhance angiography or CT imaging. Such fluids may also be used in other modalities, such as intravenous pyelogram (IVP) and cardiology. The injectors used in these procedures are often automated devices that expel the fluid from a syringe, through a tube, and into the subject.
Injectors suitable for these applications generally include relatively large volume syringes and are capable of producing relatively large flow rates and injection pressures. For these reasons, injectors for such applications typically include large, high mass injection motors and drive trains. These are typically housed in an injection head, which is supported by a floor, wall, or ceiling mounted arm. Certain such injectors include the CT9000 ADV and the Optistar MR Injection System (K948088). Such devices are generally designed to meet both the ordinary needs of the market as well as advanced needs.
There exist many drawbacks to the large injector units described above, which are presently used to inject contrast media and other media. For example, these large power injectors generally are only available at a high cost. In many instances, this cost is prohibitive in that it prices many of these injectors out of the range of some small hospitals, and out of the range of developing and third world markets. This results in patients that either (1) do without tests and treatments which may be necessary, or (2) endure the burden of travel, often over long distances, to reach those facilities with the necessary injection capabilities. Also, this results in injection procedures wherein the contrast media, or other fluid, is delivered by a hand syringe, which is ergonomically unsafe and can lead to cumulative stress disorders for the user. Further, the use of a hand syringe provides inferior images as compared to those generated when using a power injector. Additionally, many costly, large injector units may include a number of features which may not be necessary for the purposes for which they are to be used at some smaller hospitals and other medical facilities. Such facilities may be better served by an injector which does not include all the numerous features of large injectors, but which might thereby be more affordable.
In addition to the cost concerns discussed above, safety concerns can arise due to the use of these large, and often complex, injectors. First, these injectors operate at a relatively high pressures, as described above. Many current power injectors have a maximum pressure limit in order to provide safety to the components of the power injector. This prevents the injector from being damaged by being subjected to forces greater than its components are rated to withstand. These injectors also allow the operator to reduce the set maximum pressure limit to provide safety to a patient or other subject to be injected. For example, access ports are inserted into patients who need medication intravenously, but whose veins cannot tolerate multiple needle sticks. Access ports that are implanted into patients cannot tolerate many of the high pressures capable of being generated by these large injectors. High flow rates and pressures can cause the implanted catheter portion of the access port to break and require surgery to remove. For example, 100 psi is generally a threshold of pressure that a typical access port is able to withstand. However, a typical large CT injector can attain pressures during delivery of media of 300 psi at all flow rates. Thus, unless the pressure of such an injector is manually reduced, the access ports in a patient can be become over-pressured and possibly fail. Limiting the pressure for the injection of fluid into an access port for a contrast study requires a technologist to reprogram the injector to reduce the pressure limit. If the technologist forgets to reset the limit to the higher setting once the application has been performed, the desired flow rates may not be achieved during injections for subsequent patients. This can result in ineffective injections and a waste of media, among other costs attendant to repeating the injection procedure.
A second safety concern regards the structure and function of the triggers of injectors. Injectors, as described above, may include a trigger lever which may be manipulated by an operator in order to dispel media or other fluid from a syringe into a subject or to pull fluid from a container and into a syringe. The triggers of these large power injectors may often operate only at a constant set speed. Once the injection has begun, it may automatically proceed to completion at a set pressure and flow rate. An operator may be generally unable to change the injection speed or rate or pressure as an injection is occurring, without actually halting the injection procedure. This lack of control over the pressure and flow rates at which an injection proceeds may raise safety issues for the patient or other subject being injected, should an incorrect pressure limit or flow rate be programmed. Likewise, halting an injection procedure can result in ineffective injections and waste of media, among other costs.
Additional problems arise when attaching a syringe to an injector. Many current injectors include a face plate, which is disposed at the forward end of the injector. To replace the syringe, the front face plate, which facilitates coupling between the syringe plunger and the plunger drive ram, is moved, the used syringe detached, and a fresh syringe attached. The syringes may be pre-filled or may be initially empty, to be filled after being attached to the injector. The plunger drive ram of the injector is disposed within the injector housing on one side of the face plate, while the syringe is attached to, and extends from, the opposite side of the face plate. When the syringe is connected to the face plate, it is substantially co-axially aligned with the plunger drive ram. The face plates used in operatively connecting the syringe to the injector may be cumbersome and time-consuming to operate.
Additionally, many injectors may include a separate console for controlling the injector. The console typically includes programmable circuitry which can be used for automatic programmed control of the injector. This may be beneficial in that the operation of the injector can be made predictable and operate in concert with the operations of other medical equipment. Thus, at least a part of the injection process may be automatically controlled. However, any filling procedure, and typically some part of the injection procedure may be performed by an operator using hand-operated movement controls on the injector head. Typically the hand-operated movement controls may include buttons for reverse and forward movement of the injector drive ram, to respectively fill and empty the syringe. In some cases, a combination of buttons is used to initiate movement of the ram or to control ram movement speed. The injector head also typically includes a gauge or display for indicating injection parameters to the operator. Unfortunately, operators have found it cumbersome to use the hand-operated movement buttons and to read the injector head gauges and displays.
Another problem that arises concerns the temperature of the media or other fluid as it is injected. It is often important, during injection procedures, that the fluid to be injected have a temperature approaching the body temperature of the subject to be injected. To accomplish this, in large injectors as described above, a warming unit may be included in the injector to raise and maintain the temperature of a fluid to a predetermined level. Often, media will be maintained at a particular temperature in a separate warming unit and subsequently attached to the injecting unit. However, any lag time involved in removing the media from its warming cradle, and attaching the syringe, and injecting the media, may result in a decrease of the temperature of the media.
Another drawback with presently used injectors is that they are generally incapable of communicating with other injectors. As a result this only allows for one injector to be programmed and/or used at a time. Thus, there is generally no ability for different injectors to operate automatically in a sequential fashion. This situation reduces the overall safety in injection procedures by requiring a technician or other medical personnel to operate and monitor potentially several different injections simultaneously or in overlapping fashion. This increases the potential for error in an injection procedure.
Additional problems with current injectors arise due to the use of multiple components which must communicate with one another during an injection procedure. Often, several components, such as the injector, a console, and a power supply, must all communicate with one another in order to correctly perform an injection.
Another problem that arises from the structure of current injectors is in attempting to maintain the correct placement of the drive ram in order to facilitate the loading and unloading of syringes to the injector. Many prior art injectors use potentiometers and/or encoders on the motor, either separately or as redundant systems, to track the location of the drive ram in relation to the housing of the injector. It is important to be able to track the position of the drive ram so that an operator can remove and replace syringes during a series of injections, while being able to rely on the drive ram being in the correct location. Some previous injectors have used linear potentiometers; others have used rotary potentiometers. However, the use of these potentiometers and redundant systems increases the required size and cost of the injectors.
Another problem found in current injectors is in the structure for ensuring that the drive ram does not rotate about its axis of symmetry during injection. If the drive ram should rotate away from its original position, it is possible that an operator would then be unable to remove and discard old syringes, and/or attach new syringes to the injector. To reduce this problem, previous injectors generally have used a cam follower operatively connected to the drive ram which moves back and forth along with the drive ram and tracks in a groove located in an inner wall of the housing of the injector in order to prevent rotation of the drive ram. However, this structure increases friction which may result in an unsmooth movement of the injector drive ram. Additionally, any groove in the housing may become blocked which also may disrupt the injection procedure.